"Hey everyone! I haven't written in a while," Simpson-Wentz, 24, says in a new posting on her MySpace Celebrity page. "Motherhood is the most fantastic experience."

She says her new son, who was born Nov. 20, "makes me laugh and smile everyday!"

Her first outing as new mom, of course, was to support husband Pete Wentz and his band. "I finally left the house for Fall Out Boy's show on Monday night, which was so good," she says. "Their new songs sound awesome live, I can't wait for their new record!"

On Tuesday, Simpson-Wentz also hit the town to attend her hubby's art exhibition, a collaboration with pal Travis McCoy entitled "Without You I'm Not Me." "It's amazing to see how many artistic outlets those boys have!" she writes. "Made me very proud."

At the art show Wentz told PEOPLE that his son was like a great adventurer. " Every time I see my son, it looks like he's landing on the moon and discovering new rocks and stuff," he said. "I mean, every time he looks at his hand, it's like he's Christopher Columbus making it across the ocean. It's pretty awesome."

As for what's next for Simpson-Wentz, she says she's looking forward to her first holiday as a mother. "I can't wait to spend it with my new family. Christmas tree goes up tomorrow!"